In general, the devices of the present invention are typically usable with components mounted on a substrate such as a PCB where such components include surface mounted devices (SMD's) and thru-hole devices, sockets, plugs, connectors, heat sinks, etc. where the component may have leads or terminals at one or more sides thereof, it being understood that the terms "leads" and "terminals" are used interchangeably hereinafter. Moreover, in general, a substrate such as a PCB includes anything not a component such as ground and voltage planes, all circuitry, laminates, conformal coatings, board stiffeners, etc.
Component operations include removal, installation, replacement, re-positioning, adding solder, removing solder, reflowing solder, curing and/or overcuring adhesives and coatings, etc. When removing or installing certain components from a substrate in certain applications of the invention, it may be desirable to heat the leads or terminals of the component in order to melt the solder associated with the leads. In such instances, the metallized castellations of a so-called leadless chip carrier would be considered the leads or terminals of the component.
When installing or removing a component, it may be necessary to melt solder associated with the leads thereof. In such instances, the solder is considered to be reflowed regardless of whether the component is being installed or removed. Moreover, although reference is made to the use of hot gas jets herein, it should be understood the invention also extends to other forms of hot gas flow suitable for solder reflow.
With the foregoing definitions in mind, the invention and the background thereof will now be described in terms of specific applications, it being understood, there is no intent to limit the invention to such applications. Rather, the scope of the invention extends to the wide variety of applications suggested by the above definitions and other applications which will occur to those engaged in this art.
With the increasing miniaturization of electronic assemblies, more electronic components are being mounted on printed circuit boards such that the spacing between adjacent components has, in many instances, become quite small (as small as 10 mils, for example). This poses a difficulty when attempting to remove and replace a defective component in that the joints of adjacent good components may be damaged. That is, in applying a hot gas to melt the solder at the leads of a defective component, the gas may also be applied to the leads of an adjacent good component. Heating of adjacent leads, at temperatures approaching, although below, the liquidus point of solder, often causes solder crystallization which weakens the solder joint and eventually leads to joint failure. Ideally, the temperature of adjacent component solder should generally remain below approximately 160.degree. C. With a safety margin, the temperature of adjacent components should remain below 150.degree. C. (302.degree. F.) for conventional, eutectic SN-63/PB-37 solder to avoid this problem.
Nozzles for use with hot gas devices to facilitate the installation or removal of components from printed circuit substrates are known. Such nozzles are disclosed in U.S. Pat. Nos. 4,605,153 and 4,659,004 both of which are assigned to the assignee of the present application and are incorporated herein by reference. The nozzles function well in their intended applications.
A primary object of the invention is the provision of an improved hot air, component installation/removal device which is capable of precisely directing the hot air jets even when the components are closely spaced.
Another characteristic of modern electronic assemblies is the wide variety of electronic components terms of types, shapes, and sizes, etc. Thus, not only is it desirable that a hot gas, component installation/removal device be capable of precisely directing hot gas jets, but also it is desirable that a single device be capable of directing such precise jets with respect to a wide variety of components. Accordingly, it is a further primary object of the present invention to provide a device of the foregoing type and improved tips for use therewith.
Devices are known in the prior art which utilize a hot gas jet such as U.S. Pat. No. 3,970,234, assigned to the assignee of the present application and incorporated herein by reference. Another device which utilizes a hot air jet is sold by Karl Leister as the "Leister Hot-Jet Hot Air Blower" and includes a large number of nozzle types removably attachable to a hot air blower to thus provide a hot air jet capability with respect to a large number of components. However, as indicated above, it is a primary object of the present invention to provide an improved hot gas jet device which avoids the need and expense of providing a large number of nozzles.
Other prior art of interest is U.S. Pat. Nos. 3,420,430; 3,868,764; 3,603,329; 3,130,286; and 4,564,134.
The foregoing objects and other objects of the invention will be apparent from a reading of the following description and claims in conjunction with the drawings.